An organic electroluminescence (“electroluminescence” will be occasionally referred to as “EL”, hereinafter) device is a spontaneous light emitting device which utilizes the principle that a fluorescent substance emits light by energy of recombination of holes injected from an anode and electrons injected from a cathode when an electric field is applied. Since an organic EL device of the laminate type driven under a low electric voltage was reported by C. W. Tang et al. of Eastman Kodak Company (C. W. Tang and S. A. Vanslyke, Applied Physics Letters, Volume 51, Pages 913, 1987), many studies have been conducted on organic EL devices using organic materials as the constituting materials. Tang et al. used a laminate structure using tris(8-quinolinolato)aluminum for the light emitting layer and a triphenyldiamine derivative for the hole transporting layer. Advantages of the laminate structure are that the efficiency of hole injection into the light emitting layer can be increased, that the efficiency of forming excitons which are formed by blocking and recombining electrons injected from the cathode can be increased, and that excitons formed in the light emitting layer can be enclosed. As the structure of the organic EL device, a two-layered structure having a hole transporting (injecting) layer and an electron transporting and light emitting layer and a three-layered structure having a hole transporting (injecting) layer, a light emitting layer and an electron transporting (injecting) layer are well known. To increase the efficiency of recombination of injected holes and electrons in the devices of the laminate type, the structure of the device and the process for forming the device have been studied.
In addition, as the light emitting material of the organic EL device, chelate complexes such as tris(8-quinolinolato)aluminum, coumarine derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives and oxadiazole derivatives are known. It is reported that light in the visible region ranging from a blue light to a red light can be obtained by using these light emitting materials, and development of a device exhibiting color images is expected (refer to, for example, Patent literatures 1, 2 and 3).
Further, devices including phenyl anthracene derivatives as a light emitting material were disclosed in Patent literature 4. Materials having naphthyl groups at the 9th and 10th positions of anthracene were disclosed in Patent literature 5. Although such anthracene derivatives were employed as a material for emitting a blue light, it has been desired to improve a lifetime of the devices.
In addition, materials having fluoranthene groups at the 9th and 10th positions of anthracene were disclosed in Patent literature 6. Although such anthracene derivatives were employed as a material for emitting a blue light, it has been desired to improve a lifetime of the devices.
Further, it was disclosed to employ a variety of anthracene derivatives as a hole transporting material in Patent literature 7. However, they have not yet been evaluated as a light emitting material.
Meanwhile, benzene derivatives having three substituent were disclosed in Patent literature 8, and bisanthracene derivatives were disclosed in Patent literatures 9 to 12. Although these derivatives were employed as a material for emitting a blue light and exhibited high heat resistance due to its high glass transition temperature, it has been desired to improve a lifetime of the devices.    [Patent literature 1] Japanese Patent Application Laid-Open No. Heisei 8(1996)-239655    [Patent literature 2] Japanese Patent Application Laid-Open No. Heisei 7(1995)-138561    [Patent literature 3] Japanese Patent Application Laid-Open No. Heisei 3(1991)-200889    [Patent literature 4] Japanese Patent Application Laid-Open No. Heisei 8(1996)-12600    [Patent literature 5] Japanese Patent Application Laid-Open No. Heisei 11(1991)-3782    [Patent literature 6] Japanese Patent Application Laid-Open No. 2001-257074    [Patent literature 7] Japanese Patent Application Laid-Open No. 2000-182776    [Patent literature 8] Japanese Patent Application Laid-Open No. 2001-192651    [Patent literature 9] Japanese Patent Application Laid-Open No. Heisei 8(1996)-12600    [Patent literature 10] Japanese Patent Application Laid-Open No. 2000-344691    [Patent literature 11] Japanese Patent Application Laid-Open No. 2004-2351    [Patent literature 12] Japanese Patent Application Laid-Open No. 2005-15420
The present invention has been made to overcome the above problems and has an objective of providing an organic EL device having a long lifetime. In addition, the present invention has an objective of providing a biphenyl derivative, which is particularly suitable as a light emitting material for the organic EL device of the present invention.
As a result of intensive researches and studies to achieve the above objective by the present inventors, it was found that it was possible to fabricate an organic EL device having a long lifetime by employing the biphenyl derivatives represented by the general formula (I) as a material for an organic EL device:

In the general formula (I), Ar1 and Ar2 represent a condensed aromatic hydrocarbon group comprising 3 rings or more, and Ar3 represents a phenyl group or a condensed aromatic hydrocarbon group comprising 2 rings or more. However, when one of Ar1 to Ar3 represents an anthracene-9-yl group, 10th position of anthracene is not a hydrogen atom.
R1 to R3 each independently represents, a substituted or unsubstituted aromatic hydrocarbon group having ring carbon atoms of 6 to 50, a substituted or unsubstituted aromatic heterocyclic group having ring carbon atoms of 5 to 50, a substituted or unsubstituted alkyl group having carbon atoms of 1 to 50, a substituted or unsubstituted cycloalkyl group having carbon atoms of 3 to 50, a substituted or unsubstituted alkoxy group having carbon atoms of 1 to 50, a substituted or unsubstituted aralkyl group having ring carbon atoms of 7 to 50, a substituted or unsubstituted aryloxy group having ring carbon atoms of 6 to 50, a substituted or unsubstituted arylthio group having ring carbon atoms of 6 to 50, a substituted or unsubstituted alkoxycarbonyl group having carbon atoms of 2 to 50, a silyl group, which may be substituted with a substituted or unsubstituted alkyl group having carbon atoms of 1 to 50 or a substituted or unsubstituted aryl group having ring carbon atoms of 6 to 50, a carboxyl group, a halogen atom, a cyano group, a nitro group, or a hydroxy group.
R4 represents, a substituted or unsubstituted aromatic hydrocarbon group having ring carbon atoms of 6 to 10, a substituted or unsubstituted aromatic heterocyclic group having ring carbon atoms of 5 to 50, a substituted or unsubstituted alkyl group having carbon atoms of 1 to 50, a substituted or unsubstituted cycloalkyl group having carbon atoms of 3 to 50, a substituted or unsubstituted alkoxy group having carbon atoms of 1 to 50, a substituted or unsubstituted aralkyl group having carbon atoms of 7 to 50, a substituted or unsubstituted aryloxy group having carbon atoms of 6 to 50, a substituted or unsubstituted arylthio group having carbon atoms of 6 to 50, a substituted or unsubstituted alkoxycarbonyl group having carbon atoms of 2 to 50, a silyl group which may be substituted with a substituted or unsubstituted alkyl group having carbon atoms of 1 to 50 or a substituted or unsubstituted aryl group having ring carbon atoms of 6 to 50, a carboxyl group, a halogen atom, a cyano group, a nitro group, or a hydroxy group.
a to d each independently represents an integer of 0 to 3.
The present invention provides an organic EL device comprising single or a plurality of organic thin film layers including at least a light emitting layer sandwiched between a pair of electrode consisting of an anode and a cathode, wherein at least one layer of the organic thin film layers contains the aforementioned biphenyl derivatives.
The present invention has been made to overcome the above problems and can provide an organic EL device having a long lifetime. Further, it is possible to provide a particularly suitable biphenyl derivative, which has an adequate long lifetime as a material for an organic EL device of the present invention.